Author + information
- Yasumi Uchida, MD∗ (, )
- Yasuto Uchida, MD,
- Nobuyuki Hiruta, MD, PhD,
- Ei Shimoyama, MD and
- Eikou Sugiyama, MD
- ↵∗Japan Foundation for Cardiovascular Research, 2-30-17 Narashinodai, Funabashi, Chiba-ken, Japan 274-0063.
We recently discovered that Fast Green dye (FG), which is used clinically in the field of ophthalmology (1), elicits a brown fluorescence color from human HDL (HDL subtype 2b, Chemicon International, Temecula, California) when fluorescence is excited at 420 ± 20 nm and emitted at 515-nm light wavelengths. This color was not exhibited by thrombi or by any of the other major known substances including proteoglycans that constitute atherosclerotic plaques, indicating that this fluorescent color is characteristic of only HDL. Human low-density lipoprotein (LDL) and lysophosphatidylcholine (LPC) exhibited a red fluorescence with FG, which was also not exhibited by any other substances
Therefore, we evaluated the feasibility of imaging of native HDL in human coronary plaques by color fluorescent angioscopy (CFA) (2) and color fluorescent microscopy (CFM) (2) using FG as a biomarker to clarify the localization of native HDL and to correlate it with plaque morphology studied by conventional angioscopy (3).
In vitro study
Figure 1 shows an excised yellow plaque studied by conventional angioscopy. Before administering FG, the luminal surface of the plaque was yellow and green in a mosaic fashion, which indicated the presence of lipids and beta-carotene (3). After administration of FG, brown and red fluorescence appeared separately in the same plaque, revealing codeposition of HDL and LDL/LPC.
By both CFA and luminal surface scan with CFM, deposition was classified as HDL alone, HDL codeposited with LDL/LPC, and LDL/LPC without HDL, and the distribution pattern of HDL was classified as spotty, patchy, or diffuse and either separate or overlapping codeposition with LDL/LPC.
The incidences of HDL, deposited alone or codeposited with LDL/LPC in 30 normal segments, 25 white plaques (early stage of plaque growth), and 25 yellow plaques (advanced stage of plaque growth), were, respectively, 33, 76, and 21 by CFA, and 43, 80, and 28 by CFM. Thus, the incidence of HDL in white plaques was significantly (p < 0.05) higher than that in normal segments and yellow plaques. The incidences of LDL/LPC were, respectively, 3%, 8%, and 52%, indicating that the incidence in yellow plaques was significantly (p < 0.05) higher than those of the other 2 groups.
By transected surface scan with CFM, the incidences of HDL in 13 normal segments with thin (≤200 μm) intima, 28 normal segments with thick (>200 μm) intima, 41 white plaques, 15 yellow plaques without necrotic core, and 20 yellow plaques with necrotic core were 30, 71, 83, 60, and 35, respectively, and those of LDL/LPC were 0, 18, 54, 66, and 50, respectively. HDL was localized to deep (>200 μm) layer of intima in normal segments and diffusely in white and yellow plaques.
In vivo study
Seven patients with stable angina (6 men and 1 woman; 61.3 ± 2.4 years of age) underwent CFA after selective intracoronary administration of 1 ml of 2% FG. The presence or absence of HDL and LDL/LPC were different segment to segment and plaque to plaque, even in a given coronary artery (Fig. 2). As was observed in the excised coronary artery, the incidences of HDL were decreased in the order of white plaques, normal segments, and yellow plaques and the incidences of LDL/LPC increased in the same order. No obvious complications were noted during and after CFA.
The results suggest that HDL begins to deposit in the human coronary arterial wall in the early stage of atherosclerosis, increases in deposits with plaque growth, but decreases in plaques at advanced stage, possibly replaced by LDL/LPC. Also, although limited to HDL subtype 2b, which is deposited within 200 μm in depth from the luminal surface, CFA using FG may be feasible for imaging of native HDL in the coronary arterial wall.
- American College of Cardiology Foundation